Functions of Drilling Fluids
Control Subsurface Pressure
The drilling fluid creates hydrostatic pressure and this saves the borehole of the well
from cave-in
An overbalanced condition occurs when the
drilling fluid exerts(оказывает)a higher pressure
than the formation pressure
An underbalanced condition occurs when the
drilling fluid exerts a lower pressure than the
formation pressure
Functions of Drilling Fluids
Cuttings transport
The drilling fluid should
be able to remove
rock cuttings from
beneath the drilling bit,
transport them up the
wellbore through
drillstring annulus
The density and viscosity of the drilling
fluid are the properties that control the
process
Functions of Drilling Fluids
Fluid-Loss Control
The drilling mud should create a thin, low-permeable filter cake to minimize liquid loss into
permeable formations. However, the filter cake should be able to filter through itself some
portions of the drilling mud to make the drilling easier.
Poor fluid-loss control can cause:
Surge - an increase in wellbore
pressure under a bit from running
into the hole
or
Swab - a decrease in wellbore
pressure under a bit from running
out of the hole
Filter cake
Functions of Drilling Fluids
Cooling and lubricating the Rotating Bit and Drillstring
The drilling mud cools and lubricates the drill string and the bit during the
drilling
The fluid should have the ability to absorb the heat generated by the friction
between metallic surfaces and formation
Functions of Drilling Fluids
Ensure Maximum Logging Information
The drilling fluid has a profound impact on the electrical and acoustical
properties of a rock. Because these properties are what logging tools measure,
it is imperative that the correct selection of wireline logging tool or loggingwhile-drilling (LWD) tool for a given drilling fluid be made.
Functions of Drilling Fluids
Transmit Hydraulic Horsepower to the Rotating Bit
The hydraulic force is
transmitted to the rotating bit
when the fluid is ejected
through the bit nozzles at a
very high velocity. In
directional-drilling operations,
the hydraulic force powers
the downhole hydraulic
motor and turns electricpower generators (turbines)
for measurementwhiledrilling (MWD) and LWD
drillstring equipment.